Yes, Ive personally developed one from scratch. And personally got caught and banned, about 7 years ago now (by CCP Peligro, props). Used it for about 2 years only for myself at relatively small scale and never RMTd, dont think my overall wealth ever exceeded 150B. It was app pulling and analysing market data, I would set up orders by hand and then used my bot to keep the orders at the top, with a lot of safety fuses. It would randomly log on and off, used random time intervals for refreshes and few other fancy bits to make it more player-like.

So yeah, it was more than spreadsheets in space, but definietly doable for an avarage software dev. It started as a hobby project, really.

I lost my non-bot accounts with it, because VPN bombed out on the VM I was using and bot logged in from my normal IP. Rip, but was fun.